It will tell you pretty much anything you want to know. If you are considering buying one - be sure and get one with FULL service records and one that has already had the evap. core replace PREFERABLY with one that is all copper - not the copper/aluminum crap that leaks again in 10 years.
Check electricals - esp. door closing assist, wiring harness (issues on '93 thru early '96 cars), rear suspension on S500 cars. AVOID the S600 unless you have deep pockets and/or a fat bank account.
I have been very satisfied with my S500 - of course I may live to eat those words. Average maintenance for me has been around $1500 a year.

Edit - Sorry, just saw that you have a W140 already.....
check oiler tubes on the '99 - valve train noise and/or lower oil pressure likely means the bottoms have blown out. Rear suspension is expensive to fix - nitrogen spheres are about $200 a piece and the valve is $375 - not sure about struts.